Inductor to control transient currents during energized bond on

ABSTRACT

A system and method using at least one inductor operatively coupled to an electrically insulating structure suppresses transient currents generated during a bond-on process by a human worker with energized electrical equipment so as to inhibit passage of the transient currents through the electrically insulating structure operatively coupled to the energized electrical equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from United States Provisional PatentApplication Nos. 62/584,003 filed on Nov. 9, 2017 and 62/585,291 filedon Nov. 13, 2017 and Canadian Patent Application Nos. 2,985,281 filed onNov. 10, 2017 and U.S. Pat. No. 2,985,262 filed on Nov. 14, 2017, allentitled, “Inductor To Control Transient Currents During Energized BondOn”. Entireties of all the applications identified in this section areincorporated herein by reference.

FIELD

Embodiments described herein generally relate to a system and method foruse with high voltage power systems such as high voltage alternatingcurrent (AC) power systems or high voltage direct current (HVDC) powersystems. More particularly, embodiments described herein relate to asystem and method for controlling transient currents generated during anenergized bond-on process with such power systems by a human worker.

BACKGROUND

Live-line working, also known as hotline maintenance, is the maintenanceof electrical equipment such as conductors, often operating at highvoltage, while the equipment is energized. In most cases, the electricalequipment is a high voltage AC or DC power system which is in anoverhead position. Live-line working is more efficient because theelectrical equipment does not need to be shut off while the maintenanceis being performed on the electrical equipment. There are severalmethods for carrying out live-line working. All these methods preventcurrent from the live electrical equipment/live parts(s) flowing througha human worker working on the live equipment. One such method is theequipotential method, which is commonly referred to in the industry asthe “barehand method”. In the barehand method, a worker is in directelectric contact with live electrical equipment. Before contact, theworker's body is raised to the same electric potential as the liveelectrical equipment, and is then held at that potential by electricconnection, while maintaining suitable insulation from the surroundingswhich are at different potentials, like the ground, adjacent theelectrical equipment. Because the worker and the live electricalequipment are at the same potential, no current flows through theworker.

The worker can be placed in the vicinity of the overhead live electricalequipment in a number of ways. One way includes placing the worker inthe vicinity of the live electrical equipment through an insulatingstructure. The insulating structure may be a ladder, scaffolding or anaerial lift platform such as the bucket of a bucket truck for containingand delivering workers to a height of the energized electricalequipment. The insulating structure insulates the worker from groundpotential.

Conventionally an aerial lift platform may include a bucket which ismounted to a truck, vehicle, or trailer chassis via a boom. The workeris located on the aerial platform, for example within the bucket. Duringoperation, the boom is extended such that the bucket, and in turn theworker, resides besides an overhead energized electrical equipmentrequiring maintenance so that the worker in the bucket can performmaintenance on the energized electrical equipment. Typically the boomhas multiple sections to allow added height and articulation of thebucket and only the final section of the boom connected to the bucket isinsulated or made of a high strength insulating material such asfiberglass or other non-conductive or dielectric material. Thus, allsections of the boom below the final dielectric section may be made of aconductive material such as steel.

As the worker approaches the overhead energized electrical equipment,for example in the bucket of a bucket truck, an arc forms between theworker and the energized electrical equipment as the worker is beingcharged to the same potential as the electrical equipment. This arc canbe debilitating, so the worker must immediately electrically bond to theenergized electrical equipment to prevent further arcing. Typically, aconducting wand is used by the worker, during the approach, to make theelectrical connection with the energized electrical equipment so as tobring the worker to the same potential as the energized electricalequipment. When the bucket and the energized electrical equipment areclose enough such that the worker can work on the energized electricalequipment, the worker, who is already at a common potential with theenergized electrical equipment, installs an electrical link such as abonding clamp between the bucket and the energized electrical equipmentso as to bring the bucket to the same potential as the energizedelectrical equipment. This bonding between the bucket and the energizedelectrical equipment is done because the buckets that are typically usedfor high voltage energized applications are metal lined or containmetallic elements to provide a Faraday cage or electrostatic screen.

It has been observed that bonding on to the energized electricalequipment creates an initial surge or transient in the current flowingthrough the energized electrical equipment. The transient may bedescribed as a “hammer” of in-rush current. It has been further observedthat the surge or transient only occurs during the bond-on process. Oncethe worker and the energized electrical equipment are at the commonpotential, the surge or transient disappears.

Based on testing, Applicant believes that the amplitude and wave shapeof this initial current surge is directly related to the resistance ofthe insulating structure enabling the worker to reach the overheadenergized electrical equipment. As one skilled in the art willunderstand, insulators tend to deteriorate over a period of time.Applicant believes that one of the main causes for insulatordeterioration is dielectric contamination. Outdoor insulators arecontinuously exposed to the environment. Consequently, contaminants suchas salt, dust, sand and other industrial pollutants tend to deposit orbuild-up on the insulator surface as a dry layer. The dry contaminantlayer becomes conductive under light wetting conditions such as lightrain or morning dew thereby reducing the dielectric performance of theinsulator. It has been observed that when the resistance of theinsulating structure or dielectric performance of the insulatingstructure is high, the amplitude of the transient surge is low. It hasbeen further observed that when the resistance of the insulatingstructure or dielectric performance of the insulating structure is low,the amplitude of the transient surge was quite high. During laboratorytesting, it was observed that the transient could have an amplitude ofhigher than 5 A and could last for 10 usec or less.

Applicant has noted that this phenomenon occurs in both AC and DC powersystems. However, Applicant believes that because of the nature of DCpower systems, this phenomenon may be substantially more dangerous in DCsystems. In DC systems, because the voltage is constant, the bond-onwill always occur at peak voltage. Further, because the voltage isconstant and since it has been observed that the transient current couldlast for a few microseconds, it is quite possible that the transientcurrent will not be contained to the area of the insulating structureclosest to the worker but could flow through the entire length of theinsulating structure.

Further, if the insulating structure is already in a compromisedcondition and if the transient current is of sufficiently high amplitudeand duration, Applicant believes that the transient current could causea complete failure of the insulating structure.

Applicant is not aware of any systems for countering or deflecting thetransient current through the insulating structure generated during thebond-on process. This phenomenon is currently accepted in the industryas a risk.

Applicant is aware of surge arresters that protect an electronic deviceconnected to an AC power line from an in-rush current. One such surgearrester is described in U.S. Pat. No. 8,786,995 to Koch et al.

SUMMARY

Embodiments described herein relate to a system which mitigates theeffects of transient currents, generated during bond-on with energizedelectrical equipment by a human worker, on an insulating structure.

Accordingly, in one aspect a system for use with overhead energizedelectrical equipment for controlling transient currents generated duringbond-on with the energized electrical equipment by a human worker isprovided. The system comprises an electrically insulating structureadapted to carry the worker at a first end of the electricallyinsulating structure and to position the worker adjacent the energizedelectrical equipment. The system further comprises at least one inductoroperatively coupled to the first end of the electrically insulatingstructure. In use, when the worker is positioned adjacent the energizedelectrical equipment and is bonding-on to the energized electricalequipment for achieving a common potential with the energized electricalequipment, the at least one inductor suppresses transient currents fromthe energized electrical equipment to thereby inhibit propagation of thetransient currents through the insulating structure.

Accordingly, in another aspect a method for controlling transientcurrents generated during bond-on with overhead energized electricalequipment by a human worker using the system described above isprovided. The method comprises using the electrically insulatingstructure, carrying and positioning the worker adjacent the energizedelectrical equipment. The method further comprises bonding-on the workerto the energized electrical equipment, whereby the at least one inductorsuppresses the transient currents from the energized electricalequipment so as to inhibit propagation of the transient currents throughthe insulating structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is graph depicting an example of the amplitude and frequency oftransient currents generated during a bond-on process with an energizedelectrical equipment by a human worker;

FIG. 2 is a schematic illustration of a bond-on process, the figureillustrating one embodiment of the system described herein;

FIG. 3 is a schematic illustration of another embodiment of the systemdescribed herein;

FIG. 4 is a schematic illustration of yet another embodiment of thesystem described herein; and

FIG. 5 is a schematic illustration of a further embodiment of the systemdescribed herein.

DETAILED DESCRIPTION

As described in the foregoing paragraphs, Applicant has observed thatduring live-line working on energized electrical equipment, transientcurrents are generated when a human worker initially bonds-on to theenergized electrical equipment. FIG. 1 depicts an example of theamplitude and frequency of such transient currents.

Embodiments described herein depict and describe the energizedelectrical equipment as an overhead energized power line or conductorand the insulating structure as the dielectric section or sections of aboom connected to an aerial lift platform such as a bucket andbucket-lift system. However, a person skilled in the art will understandthat the energized electrical equipment may include components otherthan power lines such as static lines, optical ground wires (OPGWs) orsubstation bus pipes and couplings or couplers associated with lines,wires or pipes. Couplings may include, but are not limited to,compression sleeves which join ends of two power lines together ordead-ends or dead end connectors which are used to attach power lines tosupporting structures such as support towers or poles.

Also, the insulating structure may be an insulating scaffolding or aladder on for example a ladder truck which enables a worker to be placedor positioned in the vicinity or adjacent an overhead energizedelectrical equipment for conducting live-line work on the electricalequipment. Such insulating ladders or scaffoldings are described anddepicted respectively in FIGS. 6 and 7 of Applicant's US PatentApplication Publication No. 2016/0356826.

The system and method described herein may be used for controlling,countering, or deflecting transient currents in high voltage AC powersystems or high voltage DC power systems.

As seen in FIGS. 2 to 4, in one embodiment, the insulating structure isan insulated section 10 of a boom 12. The insulated section is made of ahigh strength dielectric or non-electrically conductive material such asfiber reinforced plastic (FRP). The insulated section 10 is connected toan aerial lift platform such as a bucket 14 at one end 10 a. Theinsulated section 10 is connected at its second 10 b to a lift systemsuch as on a boom truck (not shown). In one embodiment, the second end10 b is connected to the truck through one or more sections, such asboom sections made of an electrically conductive material such as steel.These electrically conductive sections of the boom have not beendepicted in the accompanying drawings, as they are well known in theprior art. A corona ring 16 may be attached proximate to end 10 a of theinsulated boom section 10 and an exterior collector band 18 may beattached proximate to end 10 b of the insulated boom section 10.

In the embodiments depicted in the accompanying drawings, the overheadenergized electrical equipment needing maintenance is an energizedtransmission power line or conductor 20. Since the embodiments describedherein are high voltage applications, the bucket 14 is preferably metallined to provide an electrostatic screen. During operation, human worker22 is located within the bucket and the boom 12 is extended so as toposition the human worker 22 adjacent the energized transmission powerline 20. In one embodiment, the energized transmission power line is aDC electrical power line having a voltage between 10,000 volts to600,000 volts. In order to bring the worker 22 to the same potential asthe energized power line 20, the worker 22 establishes an electricalconnection with the energized power line 20 using a bonding wand 24.Further, after the worker 22 brings himself within a suitable workingdistance of the energized power line, the worker, who is now at the samepotential as the energized power line 20, brings the bucket 14 to thesame potential as the energized power line 20 by installing anelectrical link such as a bonding clamp 26 between the bucket 14 and theenergized power line 20.

As explained in the background, during bond-on with the energized powerline, transient currents are generated. In order to control or counterthese transients, in one embodiment and with reference to FIGS. 2 to 4,at least one inductor is operatively coupled to at least the insulatedsection 10 of the boom. The inductor arrests or suppresses the transientcurrents thereby inhibiting the transient currents from propagatingthrough the insulated section 10 of the boom. As one skilled in the artwill understand, an inductor resists any change in current due itsself-inductance. Since the transient currents generated during anenergized bond-on are a change in current, the inductor will resist thischange. The at least one inductor will resist the transient currents andwill suppress the transient currents. After the transient currents diedown, the inductor will have a low resistance to the steady currentsflowing through the energized power line 20. The suppression of thetransient currents by the inductor inhibits propagation of the transientcurrents through the insulated section 10 of the boom 12 therebypreventing complete breakdown of the insulated section 10 of the boom 12and maintaining integrity of the insulated boom section 10.

The Applicant has contemplated various ways for operatively coupling theat least one inductor to the insulated boom section 10 of the boom 12.

In one embodiment and with reference to FIG. 2, the insulated boomsection 10 is a hollow boom section housing one or more operatingcomponents 24 such as a leveling rod, hydraulic line or fiber opticcable. Each of the one or more operating components 24 is alsooperatively coupled to the bucket 14. In this embodiment, each operatingcomponent 24 is associated with an inductor 50. The inductor 50 isplaced in series with the operating component 24, between the operatingcomponent 24 and the bucket 14.

In another embodiment and with reference to FIG. 3, again the insulatedboom section 10 is a hollow boom section housing a plurality ofoperating components 24. In this embodiment, the plurality of operatingcomponents 24 is connected together at a connection point 30 and theinductor 50 is positioned so as to be in series with the connectionpoint 30, between the connection point 30 and the bucket 14.

In another embodiment and with reference to FIG. 4, the insulated boomsection 10 is a solid or hollow boom section with no operatingcomponents housed therein. In this embodiment, the inductor 50 ispositioned so as to be placed operatively coupled to the insulatedsection at its end 10 a.

As one skilled in the art will understand, an inductor is a coil ofwire, which through the turns in the wire creates an inductance thatresists changes in current. As such the inductor 50 described herein maybe constructed using a cooper wire of sufficient gauge and turns. In oneembodiment, the inductor 50 may be an air core inductor. In anotherembodiment, the inductor may be a flat conductor.

In the embodiment of FIG. 4, the inductor 50 may be mounted or laminatedonto an outer surface of the insulated boom section 10 at its end 10 a.

Further, as one skilled in the art will appreciate, selection of theinductor 50 will depend on the voltage of the energized electricalequipment. For example, based on testing, it has been determined thatwhen the energized DC electrical power line has a voltage between200,000 volts to 500,000 volts, an inductor having an inductance of 100pH or above reduces the transient currents generated during energizedbond-on by at least a factor of ten or greater depending upon theinductance of the inductor.

In another embodiment and with reference to FIG. 5, Applicant hascontemplated incorporating the inductor 50 in the bonding wand 24 so asto suppress the transients. Typically, a bonding wand includes aconductive hook and an insulated gripping portion. The conductive hookis connected to the basket 14 by a cable (not shown). In thecontemplated embodiment, the inductor 50 is placed in series with theconductive hook, between the conductive hook and the gripping portion.

In use, the boom 12 including its insulated section 10 is manipulated soas to position the insulated section 10, bucket 14 and worker 22adjacent the energized power line 20. The insulated section 10 is or hasbeen operatively coupled to an inductor 50 using one or a combination ofthe arrangements described above. The worker 22 is brought to thevoltage potential of the energized power line 20 by the worker 22contacting the energized power line 20 with for example a bonding wand24 and attaching the bonding clamp 26 between the energized power line20 and the bucket 14. During the bonding-on process, the inductor 50suppresses the transient currents generated and thereby inhibitspropagation of the transient currents through the insulating section 10of the boom 12.

1. A system for use with overhead energized electrical equipment forcontrolling transient currents generated during bond-on with theenergized electrical equipment by a human worker, the system comprising:an electrically insulating structure adapted to carry the worker at afirst end of the electrically insulating structure and to position theworker adjacent the energized electrical equipment; at least oneinductor operatively coupled to the first end of the electricallyinsulating structure; and wherein, in use, when the worker is positionedadjacent the energized electrical equipment and is bonding-on to theenergized electrical equipment for achieving a common potential with theenergized electrical equipment, the at least one inductor suppressestransient currents from the energized electrical equipment to therebyinhibit propagation of the transient currents through the insulatingstructure.
 2. The system of claim 1, wherein the insulating structureincludes at least one insulated section of a boom connected to an aeriallift platform at the first end and connected to a lift system via asecond end, and wherein the at least one inductor is operatively coupledto the at least one insulated section at the first end.
 3. The system ofclaim 1, wherein the insulating structure includes at least oneinsulated section of a boom connected to an aerial lift platform at thefirst end and connected to a lift system via a second end, the at leastone insulated section housing at least one operating component which isoperatively coupled to the aerial lift platform, and wherein the atleast one inductor is placed in series with the at least one operatingcomponent.
 4. The system of claim 1, wherein the insulating structureincludes at least one insulated section of a boom connected to an aeriallift platform at the first end and connected to a lift system via asecond end, the at least one insulated section housing a plurality ofoperating components which are connected to the aerial lift platformthrough a connection point and wherein the at least one inductor isplaced in series with the connection point.
 5. The system of claim 2,wherein the operating component is a hydraulic line, a levelling rod ora fiber optic cable.
 6. The system of claim 1, wherein the energizedelectrical equipment is an energized DC electrical power line having avoltage between 10,000 volts to 600,000 volts, inclusive.
 7. The systemof claim 1, wherein the at least one inductor is an air core inductor.8. The system of claim 2, wherein the at least one inductor is a flatconductor.
 9. The system of claim 8, wherein the at least one inductoris laminated onto an outer surface of the at least one insulated sectionat the first end.
 10. The system of claim 6, wherein when the energizedDC electrical power line has a voltage between 2000,000 volts to 500,000volts, an inductance of the at least one inductor is at least 100 pH.11. A method for controlling transient currents generated during bond-onwith overhead energized electrical equipment by a human worker using thesystem of claim 1, the method comprising: using the electricallyinsulating structure, carrying and positioning the worker adjacent theenergized electrical equipment; bonding-on the worker to the energizedelectrical equipment, whereby the at least one inductor suppresses thetransient currents from the energized electrical equipment so as toinhibit propagation of the transient currents through the insulatingstructure.
 12. The method of claim 11, wherein the electricallyinsulating structure includes at least one insulated section of a boomconnected to an aerial lift platform at the first end and connected to alift system via a second end, and wherein the operatively couplingcomprises operatively coupling the at least one inductor to the at leastone insulated section at the first end.
 13. The method of claim 11,wherein the insulating structure includes at least one insulated sectionof a boom connected to an aerial lift platform at the first end andconnected to a lift system via a second end, the at least one insulatedsection housing at least one operating component which is operativelycoupled to the aerial lift platform, and wherein the operativelycoupling comprises placing the at least one inductor in series with theat least one operating component.
 14. The method of claim 11, whereinthe insulating structure includes at least one insulated section of aboom connected to an aerial lift platform at the first end and connectedto a lift system via a second end, the at least one insulated sectionhousing a plurality of operating components which are connected to theaerial lift platform through a connection point, and wherein theoperatively coupling comprises placing the at least one inductor inseries with the connection point.
 15. The method of claim 11, whereinthe insulating structure includes at least one insulated section of aboom connected to an aerial lift platform at the first end and connectedto a lift system via a second end, the aerial platform including metalcomponents, and wherein the step of bonding-on comprises the workercontacting the energized electrical equipment with a bonding wand andattaching an electrical link between the energized electrical equipmentand the aerial lift platform.